Catheters are used in a variety of procedures to treat vascular maladies throughout the body. Catheters are used to place various treatment materials, drugs, and devices within remote regions of the human body. Catheters with distal balloons are used to treat narrowed regions in the arterial system via percutaneous translumenal coronary angioplasty (PTCA) by expanding the balloon in the region of the plaque narrowing the lumen and pressing that plaque into the vessel wall.
In virtually any of these catheters, the distal end is more flexible than the proximal end and, in the more sophisticated designs, these may be intermediate regions of intermediate flexibility. The construction of these devices has become increasingly more complicated. Catheter construction now often involves multiple layers of tubing, inclusion of braided stiffeners, coil stiffeners and the like. Coaxial inclusion of dissimilar materials such as polyimide tubing has also been the practice. Simplicity has not been the watchword of modern catheter construction. In particular, catheters using distal balloons (such as the PTCA catheter mentioned above) are even more complicated because of the need to include independent tubing with which to fill and to deflate the distal balloon.
U.S. Pat. No. 3,752,617, to Burlis, shows a method and apparatus for producing tubing having different characteristics along its axial length. In general, it shows procedures for making tubing either of a single composition of a mixture of polymers or tubing having coaxially placed inner and outer layers. The patent also suggests methods for changing the physical properties of the tube as it is extruded. In the first variation, there are two extruders, one for homogenizing and delivering a first polymer to a mixing die and a second extruder for homogenizing and delivering a second polymer to the same mixing die. A sequencing control provides, at various time intervals, an increased flow from one of the extruders and a proportionally increased flow from the other extruder. The mixture of the two polymers passes through the die and results in an extruded tubing having varying physical parameters along its axial length.
The second procedure involves a composite extrusion die which produces a tube having sections of exclusively one polymer and other sections of exclusively another polymer with intermediate sections having inner portions of one and outer portions of the other polymer.
U.S. Pat. No. 4,211,741, to Ostoich, also shows a method for extruding laminated medical-surgical tubing. In particular, the tubing is coextruded, multiple-layered medical tubing having a first layer of relatively inexpensive plastic material such as polyvinyl chloride and a second layer of polyurethane. A variation described therein shows the additional extrusion of polyurethane in a third layer onto the two-layer tubing mentioned just above.
U.S. Pat. No. 4,385,635, to Ruiz, shows an angiographic catheter having a soft, flexible, pliable leading tip zone, a main reinforced length, and an intermediate zone between the tip zone and the main length. The main length is made up of a polyamide such as Nylon, and the intermediate zone contains a polyamide which is tapered distally and is jacketed by polyurethane. The soft tip is wholly polyurethane. No procedure is given for producing the device disclosed there.
U.S. Pat. No. 4,775,371, to Mueller, Jr., shows a balloon catheter having a multilayered shaft. The shaft may be structured in such a fashion that the various layers taper axially in one fashion or another, typically to permit the distal section to be more flexible than the proximal section. However, rather than being coextruded, the various layers are independently extruded. The outer layer is of a polymer which may be shrunk onto the inner layer after placement on that inner layer.
U.S. Pat. No. 4,904,431, to O'Maleki, shows a method for manufacturing soft-tip catheters having inner rigid polymer layers and soft outer polymer layers. The procedure, however, involves the independent extrusion of the inner sheath with a separate pulling speed so to create depressions or breaks in the inner polymer layer. The inner polymer layer is fed to another extruder having an independently variable pull rate to extrude the softer material onto the outer surface of the inner layer. Wire meshes and the like may be introduced into the device at desired positions.
U.S. Pat. No. 4,994,047, to Walker et al., shows a swellable cannula formed of concentric inner and outer hydrophilic and substantially non-hydrophilic layer structures. A multilumen cannula is shown in FIG. 7 of the patent. The device does not appear to change in flexibility along its axial length. Further, it is not altogether clear what the procedure for creating the device is. The single description (column 9, lines 25-35) appears to suggest that co-extrusion was the chosen procedure.
U.S. Pat. No. 5,085,649, to Flynn, shows a multilayered catheter tubing material. The tubing is shown to have an inner layer of constantly diminishing thickness and an outer layer of constantly increasing thickness, resulting in a catheter body having a consistent diameter along its length. It is said (at column 4, lines 52 and following) that the material is made by discharging from an inner annular orifice of a bi-orifice extrusion head, a first inner resin layer and also discharging from a concentric outer annular orifice of the extruder head, an outermost resin layer. The feed rate of the first resin is supplied at a constantly decreasing rate, and the second resin is supplied to the extruder at an increasing rate inversely proportional to the declining rate of the first. The bi-orifice extrusion head is of the type shown in U.S. Pat. No. 4,282,876. No suggestion of multiple lumen material is shown.
U.S. Pat. No. 5,125,913, to Quackenbush, describes a double-layer medical catheter having an integral soft tip made by the co-extrusion of a relatively rigid inner layer and a relatively soft outer layer. The extrusion equipment is operated in such a fashion so to interrupt the supply of the material for the inner, relatively soft layer so to cause a periodic void in the inner wall as the assembly is extruded. The act of interrupting the supply is said to cause a ramp in inner wall thickness at the leading edge of each void. The void is then cut to produce two soft-tipped catheters.
This invention is a continuously extruded, multilumen catheter and catheter body which involves changes in physical parameters such as flexibility or lubricity from one end of the body to the other.
U.S. Pat. No. 5,533,985, to Wang, describes several configurations of differential stiffness tubing. This disclosure describes a differential stiffness multilayer tubing configuration embodiment wherein an outside layer and an inside layer both extend the full length of a catheter. A stiff material forms the inside layer which is significantly thicker in the proximal section than in the distal section, gradually decreasing in thickness toward the distal end. A soft material forms the outside layer which is significantly thinner in the proximal section than in the distal section, gradually increasing in thickness toward the proximal end. This configuration may be described as an inverse taper configuration wherein two layers taper inversely to produce a catheter of relatively constant overall thickness dimensions.
None of the documents cited above describe devices having the construction of the inventive catheter described below.